well, what about auth gated private relays and something like 0xChat or similar with group chats?

probably just a matter of a few features involving catching code fences with their language designators and allowing you to copy them out with one click right?

the control locus is whoever runs the relay, so i'm not sure exactly how that fits into your requirements, but it's there anyhow

also, more generally, nostr clients like nostrudel already in some cases have streaming rendering like the DM view, which could easily be adapted to be the full tree structure so you can trace threads of replies and have them pop up in real time